1. Field of the Invention
The present invention generally relates to a valve, in particular, to an infusion device having a valve for draining a liquid in a flow path within an infusion device.
2. Description of Related Art
FIG. 3 is a view illustrating a flow path in an embodiment of an infusion device according to the prior art. The infusion device transports a mobile phase solution in liquid chromatography. The infusion device 10 allows a plunger 11 to go backward (leftward in the figure) for drawing the mobile phase solution by suction into a pump chamber 12, then allows the plunger 11 to go forward (rightward in the figure) for ejecting the drawn mobile phase solution. Check valves 13 for preventing a reverse flow during the suction/ejection operations are disposed at an upstream (a suction opening) side and a downstream (an ejection opening) side of the pump chamber 12
The mobile phase solution ejected from the infusion device 10 is transported to the downstream side through an analysis flow path. At the downstream side, a sample introduction device 20, a column 30, and a detector 40 are disposed. A sample, as an analysis object, is introduced from the sample introduction device 20 into the analysis flow path through which the mobile phase transported from the infusion device 10 flows. Then, the sample is separated in the column 30 according to components thereof, and detected by the detector 40 for sending out different signals according to properties of the components. On the other hand, in a flow path that branches from the analysis flow path, a pressure sensor 14 for monitoring a pressure of the liquid transported from the infusion device 10 to the analysis flow path, a damper 15 for suppressing a pressure variation of the transported liquid, and a drain valve 16 are disposed. The drain valve 16 is opened when exchanging the mobile phase solutions, so as to exchange the solution within the infusion device 10. Alternatively, the drain valve 16 is opened when releasing the pressure as the pressure sensor 14 senses an abnormal pressure, so as to drain the mobile phase solution transported from the infusion device 10 instead of introducing it into the analysis flow path. The drain valve 16 is normally closed in a blocking state. Patent Document 1 has disclosed a detailed construction of this flow path.
Further, the drain valve 16 is a valve for opening/closing a communication drained from the flow path by a rotation operation. FIG. 2(a) is a sectional view taken along a rotary shaft of a valve shaft. The drain valve 16 is connected thereon with the flow path that branches out from the analysis flow path, and thus the drain valve 16 has a flow inlet 52i and a flow outlet 52o on a main body 51 thereof. On the other hand, a shaft 54 having a valve body 53 made of resin at a front end thereof goes into and out of the space inside the main body 51 by the rotation operation; thus, the shaft 54 is formed into a structure that makes the valve body 53 disposed at the front end of the shaft 54 separated from or connected to the flow inlet 52i. In addition, in order to keep the liquid from leaking from a gap between the shaft 54 and the main body 51 when the drain valve 16 is opened, a ring seal 55 is disposed on the shaft 54. In addition, a knob 56 is disposed to perform the rotation operation on the shaft 54. The knob 56 is fixed by a screw 58 screwed into a screw hole 57 penetrating through the shaft 54. The shaft 54 supported by a screw mechanism 60 of the main body 51 goes in and out by the rotation operation on the shaft 54.    [Patent Document 1] Japanese Patent Laid-Open Publication No. 7-83400
In the structure shown in FIG. 2(a), the shaft 54 is rotated by the rotation operation; hence, the valve body 53 at the front end is rotated following the rotation of the shaft 54. Therefore, the valve body 53 is pressed to the flow inlet 52i while being rotated, and the sealing capability becomes worst. If the rotation operation is performed under the state, in which the valve body 53 abuts against the flow inlet 52i further towards a close direction, a pressing force that presses the valve body 53 towards the flow inlet 52i is applied, thereby enhancing the tightness. However, the flow inlet 52i is rubbed against the valve body 53, in which the valve body 53 becomes deteriorated, and thus the lifespan of the valve body 53 is shortened. For this reason, as shown in FIG. 2(b), the following construction is considered. That is, the shaft 54, a sealing portion 54a including the valve body 53, and a shaft portion 54b are manufactured to be separated from one another and capable of clamping a slip ring 59. Through this construction, the sealing portion 54a does not follow the rotation caused by the rotation operation on the shaft portion 54b, thereby suppressing the abrasion of the flow inlet 52i and the valve body 53.
However, in the construction in FIG. 2(b), when opening the flow path that leads to a waste liquid flow path, the shaft portion 54b is moved to an opposite side (upside in the figure) of the sealing portion 54a, thereby not applying any force to the sealing portion 54a. Thus, the sealing portion 54a remains in the space inside the main body 51, and it takes time to detach the sealing portion 54a. On the contrary, even if the liquid flows out of the infusion device, most of the liquid from the flow inlet 52i flows toward the flow outlet 52o if the extent to which the valve body 53 being separated from the flow inlet 52i equals the extent to which the flow inlet 52i and the flow outlet are spatially communicated. As a result, a separation of the sealing portion 54a from the space inside the main body 51 by pushing the sealing portion 54a upward cannot be expected. Much attention should be paid in the operation since the construction is formed of parts having strictly managed tolerances. Considering such situation, the operator of the device does not carry out the maintenance operation on the drain valve 16 easily, such that something abnormal is likely to occur to the equipment.
In view of the above, the drain valve, the shaft portion, and the sealing portion are preferably disposed to be separated from one another to ensure a degree of freedom in a respective rotation direction thereof, and preferably to ensure a fixed position relationship there-between when moving in a direction along the rotated shaft. Furthermore, a simple processing is expected instead of a complex mechanism.